Core N - Neurones

Question 0

The drug nicotine has a similar structure to acetylcholine.

Suggest the effects on brain neurones of inhaling nicotine from a cigarette. (2)

Answer 0

• Fits into membrane receptors
• Not broken down by enzymes
• Action potentials generated for a long time in post-synaptic neurone
• Causes release of other transmitters / stimulant and depressant

Question 1

Outline the role of mitochondria in synaptic transmission. (3)

Answer 1

Produces ATP for
• ACh production
• Vesicle formation
• Vesicle movement
• Exocytosis
• Functioning of ion pumps

Question 2

Events of a cholinergic synapse in order.

Answer 2

• Nerve impulse reaches presynaptic membrane
• Calcium ion channels open in presynaptic membrane
• Calcium ions enter presynaptic neurone knob
• Vesicles of acetylcholine move towards presynaptic membrane
• Vesicles fuse with presynaptic membrane and release acetylcholine into synaptic cleft
• Acetylcholine diffuses across cleft
• Acetylcholine binds to receptor proteins on post synaptic membrane
• Receptor proteins change shape, channels open and sodium ions enter post synaptic neurone
• Post synaptic membrane becomes depolarised
• Nerve impulse generated in post synaptic neurone

Question 3

Explain how synapses ensure one-way transmission of nerve impulses. (2)

Answer 3

• Vesicles found only in presynaptic neurone (ACh released only from presynaptic neurone)
• Receptor proteins found only on post synaptic membrane

Question 4

It is believed that the number of synapses between brain and neurones increases.
Suggest the advantages of this increased number of synapses. (2)

Answer 4

• Allows more interconnection of nerve pathways
• For memory
• Allows wider range of responses
• Summation

Question 5

Explain how the structure of a sensory neurone can enable the action potentials to reach the brain very quickly. (2)

Answer 5

• Myelin sheath insulates axon
• Depolarisation / action potentials only at nodes of Ranvier
• Saltatory conduction

Question 6

Natural painkillers called endorphins are similar in shape to painkilling drugs such as morphine.
There are morphine receptors on the presynaptic membrane.
Suggest how endorphins act to reduce pain. (4)

Answer 6

• Impulse causes release of endorphins
• Endorphins attached to morphine receptors
• Stops ACh release
• No binding of ACh on receptors
• In post synaptic membrane
• Fewer action potentials to pain centre in brain
• Calcium ions originally bind to receptors to cause ACh release

Question 7

Describe how a resting potential is maintained in an axon. (9)

Answer 7

• Axon phospholipid bilayer impermeable to potassium and sodium ions
• Sodium - potassium pump
• Transmembrane, globular, presence of ATP binding site
• Active process (ATP used)
• 3 Na+ pumped out, 2 K+ pumped in
• K+ diffuse out, Na+ diffuse in
• Through protein channels / transport protein
• More K+ channels open than Na+ channels
• Therefore membrane more permeable to K+ (more K+ leave than Na+ enter)
• Inside relatively more negative than outside
• -65mV
• Leaking K+ responsible for resting potential
• Electrochemical gradient
• Voltage gated channels closedo

Question 8

Describe, using named examples, how sensory receptors in mammals generate action potentials. (6)

Answer 8

• Respond to stimuli
• Some receptors are the ends of sensory neurones
• Some receptors are cells
• They are energy transducers
• Stimulus causes sodium ion channels to open
• Sodium ions enter cell
• Depolarisation
• Receptor / generator potential
• If receptor potential greater than threshold then action potential generated (all or nothing principle)
• Increased stimulus strength leads to increased frequency of action potentials

Examples:
• Rods / cones, light
• Taste buds, chemical
• Corpuscle, pressure
• Hair cells in cochlea, sound